MSK-25 · MSK Ultrasound and Joint Injection

MSK Ultrasound and Joint Injection. Part of the Musculoskeletal series of the Reflex PM&R Board Review podcast. Audio corrections: (1) In the audio: A joint injection, however, primarily threatens only the microscopic patch of tissue sitting directly at the tip of your needle. — Correct: Most of the risk is local, but a single intra-articular corticosteroid injection has real systemic effects: facial flushing, transient hyperglycemia and HPA-axis (adrenal) suppression. Repeated or high-dose injection adds osteoporosis, steroid arthropathy and avascular necrosis, and repeated intra-articular triamcinolone accelerates cartilage volume loss with no added pain benefit. (2) In the audio: as it raises diagnostic accuracy to roughly 88 percent — Correct: The 88 percent is a needle-placement rate, not the diagnostic accuracy of the block. Landmark technique lands the needle in the sacroiliac joint about 22 percent of the time; ultrasound guidance places it intra-articularly in about 88 percent of joints; fluoroscopy with contrast is the reference standard for confirming placement. (3) In the audio: the five test provocation cluster for SI joint pain ... the Patrick or Faber test, the Gaenslen's test, the thigh thrust test, the sacral compression test, and the sacroiliac distraction test ... three or more positive tests out of the five — Correct: The validated cluster is four tests, not five: distraction, thigh thrust, compression and sacral thrust, with two of four positive giving about 88 percent sensitivity and 78 percent specificity. Gaenslen adds little and can be dropped; the Patrick (FABER) test is not part of the validated cluster. (4) In the audio: particulate steroid reaching the artery of Adamkiewicz, usually left-sided between T9 and L1, causes embolic cord infarction and paraplegia — Correct: That is the wrong vessel for a cervical injection. The artery at risk differs by territory. In the cervical spine the danger is the vertebral artery and the cervical radiculomedullary feeders to the anterior spinal artery, and the catastrophe is posterior circulation stroke or cervical cord infarction. The artery of Adamkiewicz (typically left-sided, T9 to L1) is the thoracolumbar vessel, and it is what makes a lumbar or thoracic transforaminal injection dangerous. The non-particulate dexamethasone rule is the same in both territories because the mechanism is the same: crystalline particulate steroid occluding a small end-artery. (5) In the audio: Specifically, the rate is one in 10,000 to one in 50,000. You need to memorize that exact range. — Correct: There is no exact range to memorize. One in 10,000 to one in 50,000 is a published range but not the only one: studies differ in denominator, surveillance window and whether a positive culture is required. Large denominator-based series put post-injection septic arthritis nearer 1 in 1,000 to 1 in 3,000, narrower reviews report 1 in 12,500 to 1 in 50,000, and arthroscopy runs about an order of magnitude higher than injection. Learn the magnitude and the rule it drives: the risk is small, the consequence is joint destruction, and a suspected septic joint is aspirated, never injected. The written chapter is correct. Full correction register: https://www.reflexpmr.com/errata. The full companion chapter and a linked board-style Q-bank set for this topic are at https://www.reflexpmr.com/read/MSK-25-a.